1. Field of the Invention
The invention in general relates to electromagnetic parallel rail launchers and particularly to a system wherein current is sequentially injected into the rails at spaced-apart locations during projectile acceleration.
2. Description of the Prior Art
An electromagnetic launcher basically consists of a power supply and two generally parallel electrically conducting rails between which is positioned an electrically conducting armature. Current from the power supply flows down one rail, through the armature and back along the other rail whereby a force is exerted on the armature to accelerate it and a payload so as to attain a desired muzzle or exit velocity. Alternatively, current condition across the parallel rails may be by a plasma or arc which creates an accelerating force on the rear of a sabot which in the bore length supports and accelerates the projectile.
In one common type of electromagnetic launcher, the power supply is comprised of a direct current homopolar generator in series with an inductive energy storage device. A firing switch is electrically connected to short the breech end of the electrically conducting rails and is in series with the power supply.
Prior to firing a projectile, the rotor of the homopolar generator is driven to a desired rotational speed at which point, with the firing switch in the closed position, current flow is established through the storage inductor. When the current through the inductor reaches a predetermined firing level, the firing switch is opened to commutate current into the projectile launching rails. In general, for a given current, the muzzle velocity of the projectile is governed by the length of the rails. If a muzzle velocity measurable in tens of kilometers per second is desired, or lower velocities but with heavier projectiles, then the length of the rails required may be hundreds of meters. Such an arrangement would experience undesirably high conducting rail ohmic losses, and therefore low energy efficiency, and the unavoidable current attenuation during projectile acceleration will result in an excessive acceleration deterioration during projectile traverse.
Accordingly, it has been proposed that a shorter rail length for a required muzzle velocity may be obtained by resupplying energy at successive locations along the rails so that close to full acceleration is attained throughout the rail length. This is accomplished by providing individual power supplies electrically connected to the rails at predetermined locations along the bore length to achieve a relatively more constant current and accordingly nearer to the maximum sustainable acceleration with minimum barrel length.
One such multi-stage arrangement utilizes capacitive power supplies to provide the necessary additional current at successive rail locations. Such capacitive power supplies are ideal in that the switch arrangement necessary to electrically connect them to the rails can be triggered to an accuracy measurable in nanoseconds. If the total energy level requirements are high, however, such capacitive power supplies are prohibitively expensive and excessively voluminous.
Another type of proposed multi-stage arrangement utilizes a more compact and less expensive homopolar generator-inductor arrangement previously described. If ultrahigh velocities are required, however, the mechanical switching arrangement utilized to commutate current into the rails cannot operate to the high degree of accuracy needed, nor are mechanical switches able to generate the high commutating voltages required for ultrahigh projectile velocities.
The present invention provides for a multi-stage arrangement utilizing inductive power supplies wherein the arrangement is self-switching so that the additional current is injected into the rails at precisely the right moment.